DXKeeper Log unexpectedly has many "LotW SENT" 'U' entries

Mark W2OR <reston2010mm-orders@...>

      Several hundred DXKeeper log entries here, representing about five percent of the total entries, unexpectedly had their LotW SENT status changed from "Y" back to 'U' (Unaccepted).   I've tried without success to get them back to the 'Y' status, a status which they had previously.  I'm stuck. 

1.  First question:  Is there a numerical limit to the number of QSOs that can be re-submitted to LotW at one time, in order to get their LotW SENT status to "Y" ??  And yes, for such re-submissions, one has to check off the "Permit uploading of QSOs already uploaded" selection in the QSL Config page.  I've tried this procedure to re-submit all at one time, without success; all 800 of these Q's remain "U".

2.  Other particulars :
~~ This has happened before on a smaller scale, periodically over the years, and usually activating the "Sync LotW QSO" button will get the "U" QSOs changed back to "Y".    But not in this case.
~~ The affected log entries are scattered in dates going back ten years when the log was initially started.
~~ A check of the "My QTH" entries for all Q's, yielded no inconsistencies.
~~ As noted above, at one time all these log entries had been accepted by LotW and had the LotW SENT "Y" status.
~~ Several dozen of the most recently logged Q's are not affected at all; all of these recent Q's are "Y".  The most recent affected "U" QSO appears on 22 July 2018.
~~ The log shows some of the "U" entries scattered, appearing alone among the "Y" entries.  Or, sometimes there are four or six in a row, chronologically.
~~ All modes and all bands are represented in this large group of "U's"
~~ Taking one "U" QSO at a time, and right-clicking "Update from LotW", will successfully change the status back from "U" to "Y".   A good omen. 
~~ Re submitting all 800+ of these "U" entries en mass to LotW has already been attempted, using the  "Permit uploading of QSOs already uploaded" Config setting.  This procedure had been used in past years, periodically, with success.  But no joy in this case.  There may be a limit to the number of re-submissions done at one time.
~~ Yes, I could use the "Adv" advanced procedure to "Modify (all) QSOs in the Log Page Display" function, but this option I would rather save as a last resort.

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